The invention relates to a seat, adjustable in height, in which the seat member and the backrest are fast with a vertical cylindrical support comprising a first threaded portion engaged in a second threaded portion carried by a vertical column fixed on a base resting on the ground, a foot-rest concentric with the common axis of the support and the column being associated in height-adjustable manner with said support or said column. In the known manner, the foot-rest is carried either by the support for the seat member, or by the column, and in all cases on the external surface thereof. As a result, this surface being exposed to external atmospheric agents, it eventually deteriorates, above all in an industrial environment, and the operation of the height adjusting means of the foot-rest cannot be readily performed.
Furthermore, the height adjusting means generally used in this case do not permit a fine adjustment of the height; further, the manipulation of this device requires the user of the seat to descend from it, then to get on it again in order to ascertain if the adjustment is suitable, as a consequence of which there is a loss of time or non-use of the adjustment means.